A heterometallic oxide film of the MM'.sub.2 O.sub.4 type, wherein M is a divalent metal and M' is a Group 13 metal, is a very useful material in the electronics field. For instance, ZnGa.sub.2 O.sub.4 is used as a low voltage phosphor material for a flat panel display device(see I. J. Hsieh et al., Journal of Applied Physics, 76, 3735-3739(1994); L. E. Shea et al., Journal of Electrochemical Society, 141, 2198-2200(1994); and U.S. Pat. No. 5,558,814); CdGa.sub.2 O.sub.4 and ZnGa.sub.2 O.sub.4 are promising materials for applications as a transparent electroconductive material (see T. Omata, N. Ueda, N. Hikuma, K. Ueda, H. Mizoguchi, T. Hashimoto, and H. Kawazoe, "New oxide phase with wide band gap and high electroconductivity CdGa.sub.2 O.sub.4 spinel", Applied Physics Letters, 62(5), 499(1993); T. Omata, N. Ueda, K. Ueda and H. Kawazoe, "New ultraviolet transport electroconductive oxide, ZnGa2O.sub.4 spinel", Applied Physics Letters, 64(9), 1077(1994)); CaGa.sub.2 O.sub.4 and CaAl.sub.2 O.sub.4 are widely used as a fluorescent material(U.S. Pat. Nos. 5,424,006 and 5,725,801); and a single crystal of BeAl.sub.2 O.sub.4 is used as a laser material when doped with chromium(see U.S. Pat. No. 5,090,019). Some of these heterometallic oxides are usually prepared in a powder form from simple oxides of constitutive elements. For example, ZnGa.sub.2 O.sub.4 powder is synthesized from a powder mixture of ZnO and Ga.sub.2 O.sub.3. However, it is difficult to prepare a high purity complex oxide, in addition to the handling difficulties in fabricating an electronic device using a high surface area powder.
Accordingly, a CVD process has been attempted in the preparation of an MM'.sub.2 O.sub.4 type oxide using vaporizable alkoxide precursors such as magnesium aluminum isopropoxide of formula Mg[Al(OPr.sup.i).sub.4 ].sub.2. However, it has been reported that this type of alkoxide precursors are prone to undergo disproportionation reactions to form higher molecular weight compounds, e.g , Mg.sub.2 Al.sub.3 (OPr.sup.i).sub.13 (see J. A. Meese-Marktscheffel et al., Chemistry of Materials, 5, 755-757 (1993)). The formation of such high molecular weight compounds causes the problem of lowering the vapor pressure of the precursor during the CVD process.
Accordingly, there has existed a need to develop a simple, efficient process for the preparation of a high purity heterometallic oxide film of the MM'.sub.2 O.sub.4 type.